U.S. Pat. No. 6,092,597 discloses a control system for an internal combustion engine having gasoline direct injection. In this control system, the fuel mass, which is to be injected, is determined from a desired value for the torque of the engine. A procedure is also presented with which this engine can be switched over between the different modes of operation. The most essential modes of operation of such an engine are an operation of the engine with charge stratification in an almost unthrottled operation as well as a throttled operation of the engine with homogeneous injection. For an engine having gasoline direct injection, it is important to determine the actual torque of the engine. This value is, for example, outputted to other control units (for example, a drive slip control) for further evaluation or is evaluated within the control system, for example, for initializing filters and, if required, for monitoring, et cetera.
U.S. patent application Ser. No. 254,582, filed Jul. 1, 1998 (German patent publication 197 29 100) discloses a model for determining the torque of an internal combustion engine having gasoline direct injection. In this model, the actual combusted fuel mass is determined on the basis of the inducted air mass, the returned exhaust-gas mass, the oxygen concentration of the exhaust gas and a conversion factor. The actual torque of the engine is derived from this computed combusted fuel mass. It has been shown that the application of this model leads, in some cases, to unsatisfactory results because additional quantities, which operate on the torque, are not considered. Furthermore, this model is not consistent. This means that the actual torque can be determined but the inversion of the model (that is, the computation of the actuating quantities of the engine in dependence upon the desired torque) is not ensured. For this reason, various models are used to determine the actual torque and to convert the desired torque so that the complexity with respect to the control of the engine is increased.
U.S. Pat. No. 5,692,471 discloses a consistent torque model with reference to an internal combustion engine having intake manifold injection. There, the torque of the engine is computed from an optimal torque, which defines the maximum torque of the engine under standard conditions, as well as from degrees of efficiency with respect to the mixture composition, the ignition angle adjustment, and the suppression of fuel injections. The optimal torque is determined in dependence upon engine rpm and engine load (charge). With the efficiencies, the influences of the deviations of the actual values from the standard conditions, which form the basis of the formation of the optimal torque, are considered. With a corresponding inversion of the model, not only the actual torque of the engine can be determined from the actuating quantities, but also the actuating quantities can be determined in dependence upon a desired torque value. This model is not limited to an engine having gasoline direct injection because additional or changing requirements are to be considered as a consequence of the different modes of operation.